1. Field of the Invention
The invention relates to a novel and improved method and apparatus for filtering the light, or enhancing color difference and/or chromaticness difference, or obtaining two- or three-band ratio criteria widely used in remote sensing applications, or acquiring two or three bands multi-spectral imaging.
2. Description of the Prior Art
For applications of band ratio criteria, including two- and three-band ratio, multi-spectral imaging system, hyper-spectral imaging system, and spectral system are used in order to get different band spectral information. Then, two- or three-band ratio criteria with different indices, which are playing a very important role in the remote sensing application due to its invariant to some geometrical factors, such as distances between imaging system and objects, angle between the optical axis of optical system and normal lines to object surfaces, and the intensity change of illumination, can be calculated with mathematic processing.
Conventional multi-spectral imaging systems are used to get two or three bands imaging in applications, such as machine vision and remote sensing.
Several separate different band illuminations were adopted for some multi-band applications of color discrimination or object identification through color discrimination. In these kinds of applications, the lights from several separate different band illuminations illuminated the object's surface.
However, all the above sensing systems that can be used to obtain two- or three-band ratio criteria or to get two or three bands imaging are complicated and expensive to some extent due to their structure, manufacture, and calibration. For the beam-splitter multi-spectral imaging system, the multi-channel beam splitter, multi-optical-paths, the respective one-band filters, and the respective optical sensors are necessary for acquiring multi-spectral imaging. In the application of several separate different band illuminations, this illumination method for color discrimination is complicated and costly, and doesn't have a good illumination performance, and is not suitable for some applications.